#include <esp_system.h> // For esp_restart()
// ...
esp_restart(); // This resets everything!
---------------------------------------------------



code how to reset iram_attr about 0 in esp32 yfs 201 with connect php mysql database by ArduinoJson
To reset an IRAM_ATTR pulse counter on an ESP32 and send the data to a PHP/MySQL database, follow this implementation. As of 2026, using ArduinoJson and IRAM_ATTR for Interrupt Service Routines (ISRs) remains the standard for reliable real-time sensor monitoring. 
1. ESP32 Arduino Code 
This code counts pulses from the YF-S201 sensor, calculates flow, sends it via a JSON POST request, and then resets the counter to zero. 
cpp
#include <WiFi.h>
#include <HTTPClient.h>
#include <ArduinoJson.h>

const char* ssid = "YOUR_WIFI_SSID";
const char* password = "YOUR_WIFI_PASSWORD";
const char* serverUrl = "http://your-domain.com";

const int flowSensorPin = 4; // GPIO 4 (D4)
volatile int pulseCount = 0; // Must be volatile

// IRAM_ATTR places the function in RAM for speed and reliability
void IRAM_ATTR pulseCounter() {
  pulseCount++;
}

void setup() {
  Serial.begin(115200);
  WiFi.begin(ssid, password);
  pinMode(flowSensorPin, INPUT_PULLUP);
  
  // Attach interrupt to pin
  attachInterrupt(digitalPinToInterrupt(flowSensorPin), pulseCounter, RISING);
}

void loop() {
  static unsigned long lastTime = 0;
  if (millis() - lastTime > 10000) { // Send data every 10 seconds
    lastTime = millis();
    
    // 1. Read and "Reset" the counter safely
    noInterrupts(); // Stop interrupts briefly to prevent data corruption
    int finalCount = pulseCount;
    pulseCount = 0; // Reset counter to 0
    interrupts();

    // 2. Prepare JSON with ArduinoJson
    StaticJsonDocument<200> doc;
    doc["sensor"] = "YFS201";
    doc["pulses"] = finalCount;
    doc["flow_rate"] = finalCount / 7.5; // Calibration factor for YF-S201
    
    String jsonString;
    serializeJson(doc, jsonString);

    // 3. Send to PHP/MySQL
    if (WiFi.status() == WL_CONNECTED) {
      HTTPClient http;
      http.begin(serverUrl);
      http.addHeader("Content-Type", "application/json");
      
      int httpResponseCode = http.POST(jsonString);
      Serial.print("HTTP Response: ");
      Serial.println(httpResponseCode);
      http.end();
    }
  }
}
Use code with caution.

2. PHP Script (post_data.php) 
This script receives the JSON, parses it, and inserts it into your MySQL database. 
php
<?php
$servername = "localhost";
$username = "db_user";
$password = "db_password";
$dbname = "esp_data";

// Create connection
$conn = new mysqli($servername, $username, $password, $dbname);
if ($conn->connect_error) { die("Connection failed: " . $conn->connect_error); }

// Get JSON data from POST
$json = file_get_contents('php://input');
$data = json_decode($json, true);

if ($data) {
    $sensor = $data['sensor'];
    $pulses = $data['pulses'];
    $flow_rate = $data['flow_rate'];

    $sql = "INSERT INTO flow_readings (sensor_name, pulses, flow_rate) VALUES ('$sensor', '$pulses', '$flow_rate')";
    
    if ($conn->query($sql) === TRUE) {
        echo "Success";
    } else {
        echo "Error: " . $sql . "<br>" . $conn->error;
    }
}
$conn->close();
?>
Use code with caution.

3. MySQL Table Structure
Run this SQL command in your database (e.g., via phpMyAdmin) to create the necessary table. 
sql
CREATE TABLE flow_readings (
    id INT(6) UNSIGNED AUTO_INCREMENT PRIMARY KEY,
    sensor_name VARCHAR(30) NOT NULL,
    pulses INT(10),
    flow_rate FLOAT,
    reading_time TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP
);
Use code with caution.

Critical Implementation Notes for 2026:
IRAM_ATTR Importance: Without this attribute, the ESP32 may crash because the ISR might try to run from Flash memory while the flash is busy writing other data.
Volatile Variables: Always declare the pulse counter as volatile to ensure the compiler reads it directly from RAM rather than a register.
Data Integrity: Use noInterrupts() and interrupts() when resetting the counter to 0 to prevent a pulse from arriving mid-calculation.